Various types of hydraulic and pneumatic control cylinders have been employed in aircraft for controlling the mechanical positioning of a number of components. Such cylinders typically require the use of separate valves to apply to exhaust the fluid pressure in the volumes of the cylinder behind and in front of the piston to cause movement of the ram or rod. It is always desirable to reduce the space occupied by the control cylinders and their associated valves, as well as to decrease the response time of the cylinder system and increase the mechanical stiffness of the cylinder.
An electro-rheological fluid is a fluid the viscosity of which changes in response to the application of an electrical field. More specifically, such a fluid has the property of becoming substantially rigid upon application of the field having a component normal to the flow direction prior to application of the field. Such fluids and their applications in clutch devices are disclosed in U.S. Pat. Nos. 2,417,850 and 2,661,596 to Winslow. Such a fluid can be a slurry of fine hydrophilic solids in a hydrophobic liquid. The detailed operation of such fluid in a viscous shear clutch is disclosed in U.S. Pat. No. 4,444,298.
A combined valve/cylinder arrangement employing electro-rheological fluid has been proposed. This arrangement uses control sleeves, the energization of which controls liquid viscosity, positioned in longitudinal alignment with the piston. This requires that the housing has a much greater length than the piston travel. This arrangement also requires multiple inlet or outlet ports, or multiple pumps for the fluid. For further information regarding the structure and operation of such a combined valve/cylinder arrangement, reference may be made to U.S. Pat. Nos. 3,416,549; 3,552,275 and 3,599,428.